1. Field of the Invention
The present invention relates to a mist recovering method and a mist recovering apparatus for recovering a mist contained in a gas, suitable for recovering, for example, sodium from an inert gas, such as argon gas, containing sodium vapor and flowing at a high flow rate through a dry cleaning apparatus having a cleaning tank in which the inert gas is blown against a spent nuclear fuel used in a sodium-cooled fast breeder to remove sodium adhering to the spent nuclear fuel.
2. Description of the Related Art
Sodium contained in a gas in a sodium mist has been recovered by either a method which solidifies sodium from a sodium mist and collects solidified sodium by a filter for recovery or a method which changes a sodium mist into sodium droplets and collects the droplets for recovery.
When recovering sodium by the former conventional method, the filter needs to be changed occasionally because solid sodium deposits on the filter and, eventually, clogs up the filter. When recovering sodium by the latter conventional method, the filter is not clogged up in a short time because sodium is collected in sodium droplets. However, the method needs another recovering apparatus below the filter because the sodium droplets are scattered again in a sodium mist from the filter. Thus, these conventional methods are unable to recover the sodium mist efficiently and require troublesome maintenance work.
A metal mist trapping method which recovers sodium in sodium droplets from a sodium mist contained in a cover gas system is disclosed in JP-B No. 8-8968 published Jan. 31, 1996. This metal mist trapping method uses a metal mist trapping apparatus having a vessel having a vertical gas passage packed with horizontal metal wire nets stacked in layers. The upstream metal wire nets with respect to the flowing direction of a gas containing a sodium mist are formed of finer metal wires and have smaller meshes than the downstream metal wire nets. The metal wire nets are heated at a temperature not lower than the melting point of sodium by a heating unit during operation. Since the gas passage of the vessel is fully packed with the horizontal metal wire nets stacked in layers, the sodium mist is trapped mainly by the metal wire nets near the gas inlet of the vessel and liquid sodium layers held on those metal wire nets enhances the sodium mist trapping performance of the metal mist trapping apparatus if the gas containing the sodium mist flows through the gas passage at a relatively low flow rate.
However, if the gas containing the sodium mist flows through the gas passage at a high flow rate at which the gas flows when a dry cleaning apparatus is used, and the size of droplets produced by the condensation of the sodium mist is as small as several micrometers, liquid sodium layers held on the metal wire nets are blown off the metal wire nets and discharged through the gas outlet of the vessel, which reduces the sodium mist recovering efficiency of the metal mist trapping apparatus.